1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method.
2. Background Art
With high integration of a semiconductor device, a circuit pattern of the semiconductor device has been miniaturized. In order to form a micro circuit pattern in the semiconductor device, a high-precision original image pattern (i.e., reticle or mask) is required. It is known that an electron beam writing apparatus having excellent resolution is used to manufacture the original image pattern.
In this type of electron beam writing apparatus, shot data is generated from write data in which the shape and position of each graphic pattern are defined. Main deflection data and sub deflection data are generated by a deflection controller in such a manner that each pattern contained in the shot data is written. The respective deflection data are DA-converted by a DAC amplifier (hereinafter abbreviated as “amp”). The so DA-converted signals are amplified and applied to a main deflector and a sub deflector, thereby writing each pattern onto a sample (refer to, for example, a patent document 1 (JP-A-2008-182073)).
A conventional shot data generating method will be explained with reference to FIG. 13.
As shown in FIG. 13, the shapes and positions of graphic patterns P1 and P2 are defined in write data D. In the conventional method, the graphic patterns P1 and P2 defined in the write data Dare divided into a plurality of subfield areas SF. Next, they are divided into graphics FG expressed in shot units within the respective subfield areas SF.
Meanwhile, it is known that writing accuracy where a graphic is shot to the center of each subfield area SF and writing accuracy where a graphic is shot to the periphery of the subfield area SF, differ from each other. Multi-pass writing has been performed to enhance the writing accuracy. The multi-pass writing is a method for overlaying graphics written in plural independent passes on one another to write a target pattern.
As the multi-pass writing, there are known a method for overlaying graphics written with each subfield area being shifted, on each other, a method for overlaying graphics written with each stripe area (see FIG. 2) being shifted, on each other, and a method for overlaying graphics written with both areas being shifted, on each other.
FIG. 13 shows an example for generating shot data in two passes with subfield areas being shifted. In the example, subfield area division corresponding to the second pass is performed so as to differ from subfield area division corresponding to the first pass.
In the conventional method, however, graphics FG subsequent to the subfield area divisions differ from one another at the first and second passes. Since shot division is performed on the graphics divided into the subfield areas, it is necessary to perform the shot division for every pass. Thus, since the shot division must be done by the number of passes, time is taken to generate shot data and writing throughput is hence degraded.
Attention is paid to the rectangular graphic pattern P1 in the example illustrated in FIG. 13. The graphic pattern is shot-divided into 6×5=30 at the first pass, whereas the graphic pattern is shot-divided into 5×5=25 at the second pass. A problem arises in that when the number of shots differs for every pass in this way, a shot dividing method grows complicated. Further, a problem arises in that the number of shots increases depending on how to perform subfield division.
In a normal electron beam writing apparatus, the estimation of the number of shots is performed as a pre-process prior to the generation of shot data, and writing time is estimated from the result of its estimation. Since the conventional shot division is based on the graphics subsequent to the subfield area division and grows very complicated as mentioned above, a huge amount of time is taken for arithmetic processing. Therefore, only a simple method can be adopted as the method for estimating the number of shots as the pre-process. As a result, a problem arises in that the shot dividing method at the pre-process stage and the shot dividing method at the shot data generation stage differ and the accuracy of estimation of the number of shots corresponding to the pre-process is degraded.